How should the varicella vaccine be administered, including dosing schedule, contraindications, and post‑exposure prophylaxis, for varicella‑naïve individuals?

Varicella Vaccine Administration

All varicella-naïve individuals aged ≥12 months should receive two 0.5-mL doses of varicella vaccine administered subcutaneously, with age-specific intervals: 3 months minimum for children <13 years (though doses given ≥28 days apart are valid) and 4 weeks minimum for persons ≥13 years. 1

Dosing Schedule by Age

Children 12 Months to 12 Years

• First dose: Administer at 12-15 months of age 1, 2
• Second dose: Routinely given at 4-6 years (before kindergarten entry), but may be administered earlier if the minimum 3-month interval is maintained 1, 2
• Critical timing note: If the second dose is inadvertently given 28 days to 3 months after the first dose, it is considered valid and does not need repeating 3, 1, 2

Adolescents and Adults ≥13 Years

• Two doses separated by 4-8 weeks (minimum 4 weeks) 4, 1
• If more than 8 weeks elapse after the first dose, administer the second dose without restarting the schedule 1
• Only single-antigen varicella vaccine should be used (MMRV is not licensed for this age group) 1, 5

Route of Administration

• Subcutaneous or intramuscular injection of 0.5 mL 1, 5
• The vaccine is heat-sensitive and requires proper storage 6

Evidence of Immunity

Individuals do not require vaccination if they have any of the following 4, 1:

• Documentation of 2 doses of varicella vaccine at least 4 weeks apart
• Laboratory evidence of immunity or laboratory-confirmed disease
• Healthcare provider-diagnosed or verified history of varicella or herpes zoster
• Exception: U.S. birth before 1980 is NOT considered evidence of immunity for healthcare personnel or pregnant women 4, 1

Contraindications

Absolute Contraindications 1, 5

• Severe allergic reaction to any vaccine component (including neomycin or gelatin) or previous varicella vaccine dose
• Immunosuppression: Do not administer to highly immunocompromised patients 7, 5
• Pregnancy: Avoid conception for 3 months following each dose 1, 5
• Active untreated tuberculosis 5
• Moderate or severe febrile illness 5

Special Populations Requiring Evaluation

• Immunocompromised patients: Evaluate immune competence before administration, especially with family history of congenital or hereditary immunodeficiency 7, 5
• Certain minimally immunocompromised patients may receive vaccine: Those with HIV without severe immunosuppression or primary immune deficiency without T-cell defects (e.g., complement deficiency, chronic granulomatous disease) can receive the 2-dose series with 3-month intervals 7
• Pre-immunosuppression timing: Administer vaccine ≥4 weeks before planned immunosuppressive therapy when possible 7

Post-Exposure Prophylaxis

Vaccine as PEP

• Most effective when given within 3 days of exposure, but can be administered up to 5 days post-exposure 8, 9
• Effectiveness: 62% in preventing any disease and 79% in preventing moderate-to-severe disease when given within 5 days 9
• Second dose as PEP: For individuals with one prior dose, administering a second dose as PEP shows 60-77% effectiveness even when given >5 days post-exposure 10, 11
• Vaccination is still recommended even beyond 5 days to help control outbreaks 10, 11

Varicella Zoster Immune Globulin (VZIG)

Indicated for populations ineligible for vaccination 12, 8:

• Immunocompromised children and adults
• Pregnant women without evidence of immunity
• Neonates whose mothers develop varicella between 7 days before delivery and 7 days after delivery (updated from previous 5 days before to 2 days after) 13
• Premature infants with significant exposure
• Timing: Administer as soon as possible, but always within 10 days of exposure (updated from previous 96-hour window) 13

High-Priority Groups for Vaccination

Special consideration should be given to 1:

• Healthcare personnel
• Household contacts of immunocompromised persons
• Teachers and childcare employees
• Residents and staff of institutional settings (including correctional facilities)
• College students and military personnel
• Nonpregnant women of childbearing age
• International travelers
• Adolescents and adults living in households with children

Important Clinical Caveats

Drug Interactions

• Avoid salicylates for 6 weeks following vaccination in children and adolescents due to Reye syndrome risk 1, 5
• Immune globulins and blood products: Should not be given concurrently; may interfere with vaccine response 1, 5
• Tuberculin skin testing: May cause temporary depression of PPD reactivity 5

Transmission Precautions

• Avoid close contact with high-risk susceptible individuals for up to 42 days post-vaccination due to possible transmission of vaccine virus, though uncommon after 21 days 7, 5

Pregnancy Management

• Prenatal assessment: All pregnant women should be assessed for varicella immunity 1
• Postpartum vaccination: Women without evidence of immunity should receive the first dose before hospital discharge, with the second dose at 4-8 weeks (coinciding with postpartum visit) 1

Catch-Up Vaccination

• Individuals who previously received only 1 dose should receive a second catch-up dose 1
• No need to restart the series regardless of time elapsed between doses 3
• Minimum intervals: 3 months for children <12 years, 4 weeks for persons ≥13 years 1